Magneto-responsive device control system



June 26, 1956 w, c, DUNLAP, JR 2,752,553

MAGNETO-RESPONSIVE DEVICE CONTROL SYSTEM Original Filed Oct. 19 1949Figl.

SUURCE IND/CD470}? 0F 0/? 5/9/41- CONT/POL VULT/YGE DEV/CE F1 .2. 5 SE j/9 24 MW, II/IA/Z7 i/ Y 2 P H Z V 4%:3/ M 20 Inventor: William CrawFordDunlap, Jr,

His Attorn ey.

United States Patent MAGNETO-RESPONSWE DEVICE CONTROL SYSTEM WilliamCrawford Dunlap, .ln, Schenectady, N. Y., as-

signor to General Electric Company, a corporation of New Zorlr Originalappiication October 19, 1949, Serial No. 122,243. Divided and thisapplication March 10, 1953, Serial No. 341,573

4 Claims. (Cl. 321-46) This invention relates to a magneto-responsivedevice system employing a semi-conductor, the electrical resistance ofwhich is controllable by a magnetic field. This application is adivision of my copending application Serial No. 122,243, filed October19, 1949, and assigned to the same assignee as the present application,now abandoned.

Known magneto-responsive systems which are capable of producing anelectrical signal output are generally of the type employing amagneto-inductive transformer having a variably excited prhnary windingor employing a magneto-inductive generator having a physicallyrelatively movable magnetic armature. In any of these magnetoinductivesystems the output voltage signal is dependent upon a rate of change ina magnetic field which is produced in the transformer by a changingcurrent in a primary winding, and in the generator by the relativemovement between the magnetic parts. However, it is often desirable toobtain an electrical signal which subsists when no change occurs andwhen no rate of change exists, but a signal which nevertheless indicatesthe magnitude of a direct current excitation signal in an apparatus withrelatively fixed parts or indicates the relative positions of relativelymovable parts, while at the same time giving an indication of magnitudeof input signal or change of relative position in terms of the magnitudeof excitation or instantaneous position in these devices.

It is, therefore, an object of my invention to provide amagneto-responsive device system which is a direct current amplifier aswell as an alternating current amplifier.

Another object of the invention is to provide a magnetoresponsive devicesystem which responds both to direct current and alternating currentsignals and which may employ a direct current or alternating currentpower source.

It is a further object of my invention to provide a magneto-responsivedevice system which may be used as a position indicator to indicate therelative positions of two relatively movable parts in terms of theelectrical resistance of an output circuit or the magnitude of anelectrical output derived therefrom.

The invention, therefore, generally comprises an arrangement including asemi-conductor element the re sistance of which is responsive to amagnetic field therethrough and an apparatus for the creation of such amagnetic field in accordance with an input signal, and lead connectionsfor the measurement of the resistance of the semi-conductor. In accordwith a further feature of the invention, the semi-conductor elementcomprises a point contact type semi-conductor rectifier having a highrectification ratio. This point contact rectifier is connected in serieswith an alternating current source to provide a simultaneousrectification and enhanced magnetoresistive control of current in thisseries circuit, whereby a unidirectional current component is producedin the impedance which varies in accord with the intensity of a magneticfield through the semi-conductor rectifier.

The features which I desire to protect are pointed out withparticularity in the appended claims. The invention itself, togetherwith further objects and advantages thereof may be best understood byreference to the following description taken in connection with thedrawing, in which:

Fig. 1 shows the magneto-responsive device system of this inventionincluding electrical circuit components which are shown schematically;and

Fig. 2 is an enlarged detail view of an embodiment of the inventionwherein the invention is used with an alternating current source and oneof the contacts with the semi-conductor element is a pointed sharpenedwire to provide a simultaneous rectification and enhancedmagneto-resistive control of the current flowing in the circuit of thesemi-conductor element.

Referring more particularly to the drawing, in Fig. 1 there is shown amagneto-responsive device system which includes a semi-conductor elementor member 2 held in a fixed position by clamping members 3. Thesemi-conductor itself may be characterized as a magneto-responsivedevice. A magnetic structure 4, with pole pieces 5 and 6, is positionedto set up a magnetic field through semi-conducting member 2. Magneticstructure 4 is adapted for movement along guides 7 and S. This movementmay occur in response to movements of a movable body 9 transmittedthrough a suitable linkage such as that comprising links 10 and 11 andlever 12. Magnetic structure 4 may be a permanent magnet or anelectromagnet with an excitation winding 13 which may be energized froma source of signal voltage 14. Suitable electrical connections to thesemi-conductor element 2 are made at 15 and 16. A resistance measuringcircuit provided at these connections comprises a source of electricalenergy such as battery 17 and a load impedance such as resistor 18 whichare connected in series with the semi-conductor element 2. The voltageof battery 17 is, therefore, impressed across the semi-conductor and theload resistor 18 in series. The relative magnitudes of the respectivevoltages across these two resistances may be measured by a device suchas an electron discharge device 19 having a control electrode 20 towhich voltage across resistor 18 may be applied. The output of device 19may be fed to an indicator or control device 21 for establishing acontrol in accordance with the input signal from source'14. Resistor 18,discharge device 19, and indicator or control device 21, constitute aunidirectional current responsive device.

In the operation of the magneto-responsive device of this invention, asuitable electrical signal which may comprise an alternating currentvoltage or a direct current voltage or a combination of the two may besupplied from signal voltage source 14 and used to energize winding 13to create a magnetic field in magnetic structure 4 in accordancetherewith. The magnetic field which then exists between pole pieces 5and 6 passes through semi-conductor element 2. Element 2 comprises asemi-conductor material, such as germanium, whose electrical resistanceis dependent upon the flux density of a magnetic field therethrough. Inthis connection it has been found that, in an element of germanium, amagnetic field flux density of 12,000 gauss causes as much as a 25%increase in resistivity over the value of resistivity with no magneticfield. Element 2 is preferably of a highly purified type of germaniumcorresponding to a bulk resistivity above 10 ohm-centimeters andcharacterized by a substantial freedom of conductive impurities such asaluminum, tin arsenic, and gallium, since the presence of theseelements, even in small amounts such as .1%, greatly lowers theresistivity of the germanium. Extremely minute traces, for example onepart per million, of such impurities will, of course, still be presenteven in germanium purified to a resistivity above 10-ohm centimeters.These minute impurity traces evidently determine the conductivity-typeof the germanium, i. e., whether the germanium is N- type or P-type, aswill be more fully explained hereinafter. High resistivity N-typegermanium is customarily employed in germanium point contact rectifiershaving a high rectification ratio, for example substantially above 100to 1. High resistivity germanium is also desired in the presentinvention because the increase of resistance of germanium in thepresence of a magnetic field, hereinafter referred to as themagneto-resistive effect, is proportional to the unmagnetizedresistivity of the material. Semi-conductors which exhibit thismagneto-resistive effect are hereinafter referred to as semi-conductorshaving magneto-resistive properties.

Element 2 is connected in series with resistor 18 and a voltage isimpressed across both by means of battery 17. Variations in theresistance of element 2 due to the magneto-resistive efiect causevariations in the proportionv of the supply voltage from battery 17which exists at a given time across element 2 and resistance 13. As aresult, the voltage at the common connection between element 2 andresistor 18 supplied to control electrode 20 of electron dischargedevice 19' fluctuates with respect to ground. The signal thusderived isamplified by electron discharge device 19 and supplied to an indicatoror control device 20. Device 20 may be any visual or audible indicatorsuitable to bring attention to the condition causing the signal fromsource 14. Alternatively, it may comprise an automatic control devicefor controllingtemperature or any other condition or functioncontrollable by an electrical voltage.

The magneto-responsive device system of this invention may also indicateor control in response to physical movements of a movable body such as9. Through a suitable linkage suchas that provided by members 10, 11 and12 movement of body 9' causes a corresponding movement of magneticstructure 4 so that pole pieces and 6 gradually assume a new position,for instance as at 5a and 6a. In this new position, the magnetic fieldprovided by magnetic field structure 4 no longer traverses thesemi-conductor element 2 and the resulting change in the resistivity ofelement 2 effects an indication or control signal at indicator orcontrol device 21 in accordance with the new position of movable body 9.

Element 2 may comprise a slab or wafer of semi-con.-

ductor material and the electrical connections at 15- andv 16 may bemade by soldering suitable conductors to the semi-conductor element atthe edges thereof. Pure tin.

solder is preferably used, although other soldering mate rials may befound to besatisfactory.

In Fig. 2 there is shown a detailed view of an embodiment oftheinvention wherein the semi-conductor element 2 comprises aconventional high rectification ratio germanium point-contact rectifier22, and an alternating current source 17a replaces battery 17 of Fig. l.Rectifier 22 comprises atubular shell 23 which may be of a nonmagneticmetallic material. A silver plug 24 having a copper conductor 25'-extending axially therethrough fills and seals one end of shell 23. Asemi-conductor pellet 26 of high resistivity N-type. germanium issoldered at the end of the copper conductor on the inner face of thesilver plug by means of a pure tin solder. The pellet may be about 0.06inch indiameter and 0.02 inch thick. Also within the shell 23 is a steelrod. 27 having a copper conductor 28 connectedv at one end, such. as byinsertion and soldering into a round hole drilled in the endthereof. Rod27 carries a pointed electrode or cat whisker 29; which may be ofPhosphor bronze, which is spot weldedto a small. projection 30upstanding from the inner end of. rod. 27. The rod: isifirmly held in,place within the shell. by an insulating bead 31. which may be of. asuperpolyamide material such as nylon.

In constructing a rectifier. of the type shown; the cat Whisker 29 isfirst welded to rod projection 30 and the nylon head is slipped. overtherod. Thereaften, therod:

and bead are press fitted into the shell in a desired position. ThePhosphor bronze cat whisker 29 may preferably be 0.0015 inch in diameterand of an overall length before bending of about 0.1 inch. It issharpened at the contact tip at 16 to provide an area of contact of theorder of 10- square inches when in contact with the surface of thegermanium pellet.

The pellet 26, after having been soldered to silver plug 24, is polishedto substantially optical smoothness on the fiat exposed surface. Thepointed tip of the cat whisker at 16 is held against the germaniumpellet with a force of about 150 milligrams under the force ofdeflection of cat whisker 29. Pole pieces 5 and 6 of magnetic structure4 are positioned to produce a magnetic field through the germaniumpellet in a manner encompassing the point contact 16, and the entireelerr ent 2 is fixedly positioned by clamping members 3.

One advantage of constructing the element 2 in the form of a rectifier22 is that the current must pass through the point of cat whisker 29 at1'6 in order to traverse the semi-conductor pellet 26. The resultingvery small area of conduction in the semi-conductor immediately adjacentto the cat whisker point greatly increases the circuit resistance at thesemi-conductor pellet, thereby proportionally increasing themagneto-resistive efiect.

Another advantage of constructing element 2 in the form of a rectifier22 is that the magneto-responsive device control system can now also beused with an alternating current power source 1711 as well aswith adirectcurrentpower source properly polarized to pass current in the easyflow direction of rectifier 22. If an alternating current source 17a isemployed, a unidirectional component of current flows through resistor18' as aresult of the rectifying action of rectifier 22, and this directcurrent component also varies inaccord with the intensity of signalsource 14 as a result of the enhanced magneto-resistive effect of themagnetic field upon the point-contacting area of rectifier 22.

Certain semi-conductors may be said to be of the negative or N type andothers of'the positive or P type. These terms are defined below.Germanium may be of either the P or N type depending upon the type ofimpurity traces present. In the generalized embodiment of Figure 1, thesemi-conductor may comprise either high resistivity N-type or highresistivity P-type semi-conductor material. However, in the embodimentshown in Fig. 2, rectifier 22 must have good rectificationcharacteristics and strongly N type high resistivity germanium ispreferably used for pellet 26 because strongly N-type germaniumpoint-contact rectifiers ordinarily have a rectification ratio severalthousand toone, while P-type germanium point-contact rectifiers aresomewhat unpredictable, often showing little or no rectification.P-t'ype germanium point-contact rectifiers may, of course, also be usedif they are found or made to have sufiicient rectificationcharacteristics substantially above to 1.

It will be appreciated that most commercially available point-contactgermanium rectifiers employ an N-type germanium. pellet highly purifiedto have a resistivity above 10-ohm centimeters and are suitable for usein connection with this invention.

The P type and N type designations for a. semiconductor may be definedas follows. If current is conducted through a semi-conductor element inone direction and a magnetic field is created through the same elementin a. direction perpendicular to the current, a voltage will beobservable between two points which are aligned in a direction.perpendicular to both the current and the magnetic field. This effectmay be observed in both conductors and semi-conductors and is generallytermed the Hall effect, the voltage generated thereby being called theHall voltage. Generally it is observed, both with conductors andsemi-conductors, that the sign of the Hall voltage is what would beexpected if negative electrons carried the conduction current and weredeflected in the magnetic field. However, many conductors andsemi-conductors, including some samples of germanium, show a reverseHall effect, as if positive particles were doing the conducting insteadof the usual negative electrons. Semi-conductors which fall within thefirst of these two classes may be designated as negative or N type, andthose in the second class as of the positive or P type.

It will be seen from the above description that this invention providesfor a magneto-responsive device system which produces a signal inresponse to, and proportional to the strength of, a magnetic field andindependent of the rate of change thereof which will provide indicatoror control voltages useful in many applications.

While only certain preferred embodiments of the invention have beenshown by way of illustration, many modifications will occur to thoseskilled in the art and it is, therefore, to be understood that theappended claims are intended to cover all such modifications as fallwithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A magneto-responsive device system comprising a germanium rectifierhaving a rectification ratio in excess of 100 to 1 and including a highresistivity germanium element and a pair of spaced connections theretofor the conduction of current therethrough, one of said connectionscomprising a metal electrode making a point contact with said elementthe order of square inches in area which produces good rectification ofalternating currents supplied between said connections, means forestablishing a variable magnetic field of high intensity through saidelement and encompassing said point contact connection to vary theresistance of said element both within the bulk of said element and atsaid point contact so that said rectifier both rectifies and controlsthe magnitude of alternating current supplied between said connections,a source of alternating voltage and a load resistance connected inseries circuit relationship with said rectifier so that the voltagedeveloped across said load resistance comprises a rectified image ofsaid alternating voltage which is varied in magnitude in accord withvariations in the magnetic field established through said rectifier.

2. The magneto-responsive device system of claim 1 in which the meansfor establishing a variable magnetic field of high intensity throughsaid element comprises a magnetic yoke having a pair of pole piecesdiposed on opposite sides of said element, and means for producingrelative movement between said magnetic yoke and said member.

3. The magneto-responsive device system of claim 1 in which the meansfor establishing a variable magnetic field of high intensity throughsaid element comprises a magnetic yoke having a pair of pole piecesdisposed on opposite sides of said element, an energizing winding onsaid magnetic yoke and a source of signal voltage connected to saidwinding.

4. The magneto-responsive device system of claim 1 in which the meansfor establishing a variable magnetic field of high intensity throughsaid element comprises a magnetic yoke having a pair of pole piecesclosely disposed to opposite sides of said element, an energizingwinding about a portion of said magnetic yoke, a source of signalvoltage connected to said winding and means for producing relativemovement between said magnetic yoke and said element, the intensity ofthe field through said element depending upon both the source of signalvoltage and the relative position between said magnetic pole pieces andsaid element.

References Cited in the file of this patent UNITED STATES PATENTS817,664 Plecher Apr. 10, 1906 1,765,607 Ohl June 24, 1930 1,810,539Sokoloif June 16, 1931 2,553,490 Wallace May 15, 1951 2,553,491 ShockleyMay 15, 1951 2,640,901 Kinman June 2, 1953 2,650,311 Bray Aug. 25, 1953OTHER REFERENCES Physical Review, vol. 74, page 976, August 15, 1948.

